Amorphous Polyamide Research Articles

Amorphous polyamide/maleated styrene–ethylene–co-butylene–styrene nanocomposites: effects of clay loading and compatibilizer content on morphology and mechanical properties

The effect of the organoclay content on the toughness of a rubbery modified amorphous polyamide (aPA)/organoclay-based nanocomposite was studied by changing the modifier (maleic anhydride) content. The dispersed rubber particle size decreased markedly with the addition of the modifier, indicating compatibilization of the nanocomposite. However, the particle size of the dispersed phase increased slightly with the organoclay content due to the interactions between the dissolved surfactant and the compatibilizer. Furthermore, we observed that the organoclay resided in the aPA matrix, and that its dispersion remained constant upon rubber addition. This resulted in materials with high stiffness and extremely large toughness values, as measured by both the standard impact strength and the essential work of the fracture method. Because the rubber content was kept constant, the inorganic part of the clay was proposed to be the main parameter that controls toughness. The impact strength of an amorphous polyamide/organoclay nanocomposite has been increased by means of a rubber modified with maleic anhydride (MAH). The organoclay resided in the polyamide matrix and maintained dispersed rubber particle size upon rubber addition. The changes of the dispersed rubber particle size with modifier and nanoclay addition indicated compatibilization of the nanocomposites and interactions between the dissolved surfactant and the rubber modifier. The obtained nanocomposites had a high stiffness and extremely large toughness values, as determined both by impact strength measurements and by the essential work of fracture method.

Elastic–plastic behavior of non-woven fibrous mats

Electrospinning is a novel method for creating non-woven polymer mats that have high surface area and high porosity. These attributes make them ideal candidates for multifunctional composites. Understanding the mechanical properties as a function of fiber properties and mat microstructure can aid in designing these composites. Further, a constitutive model which captures the membrane stress–strain behavior as a function of fiber properties and the geometry of the fibrous network would be a powerful design tool. Here, mats electrospun from amorphous polyamide are used as a model system. The elastic–plastic behavior of single fibers are obtained in tensile tests. Uniaxial monotonic and cyclic tensile tests are conducted on non-woven mats. The mat exhibits elastic–plastic stress–strain behavior. The transverse strain behavior provides important complementary data, showing a negligible initial Poisson's ratio followed by a transverse:axial strain ratio greater than −1:1 after an axial strain of 0.02. A triangulated framework has been developed to emulate the fibrous network structure of the mat. The micromechanically based model incorporates the elastic–plastic behavior of single fibers into a macroscopic membrane model of the mat. This representative volume element based model is shown to capture the uniaxial elastic–plastic response of the mat under monotonic and cyclic loading. The initial modulus and yield stress of the mat are governed by the fiber properties, the network geometry, and the network density. The transverse strain behavior is linked to discrete deformation mechanisms of the fibrous mat structure including fiber alignment, fiber bending, and network consolidation. The model is further validated in comparison to experiments under different constrained axial loading conditions and found to capture the constraint effect on stiffness, yield, post-yield hardening, and post-yield transverse strain behavior. Due to the direct connection between microstructure and macroscopic behavior, this model should be extendable to other electrospun systems and other two dimensional random fibrous networks.

Morphology evolution of miscible blends between crystalline PA6 and amorphous PA6IcoT

The morphology evolution of miscible blends of a semicrystalline polyamide 6 (PA6) and an amorphous polyamide 6Ico6T (PA6IcoT) was investigated using an internal Brabender mixer at a temperature range 220–260°C. Morphology of the blends was characterized by scanning electron microscopy (SEM) and laser particle analysis. Temperature rising dissolution was used to separate the different phases of the blends and the phase compositions were determined by Fourier transform infrared (FTIR) spectroscopy. The particle size evolution of the dispersed phase (PA6) was calculated and agreed well with experimental observation. It was found that the particle size was quickly reduced to nanometer scale after several minutes of processing. A convection-diffusion model was adopted to study the phase evolution during melt–melt mixing stage and compute the dimension of each phase. The results strongly support the notion of existence of distinct phases during blending, whose development can be well described by the model. The dispersed phase is reduced mainly by stretching of flow, while the broadening of the blending phase can be primarily attributed to molecular diffusion. The study also suggests the possibility to prepare novel polymer blends with nanometer sized domain of high uniformity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Toughened and stiffened nanocomposites based on an amorphous polyamide modified with both styrene/ethylene-co-butylene/styrene triblock copolymer and an organoclay

Polymer nanocomposites (PNs) based on an amorphous polyamide (aPA) modified with both a maleated rubber (mSEBS) for toughening, and with an organically modified organoclay for stiffening were obtained in the melt state. The PNs were highly dispersed and the organoclay was exclusively located in the aPA matrix. However, they showed a fine particle size that was larger than that of the corresponding blends. This indicates a lower compatibilization in the PNs that was attributed to a slight surfactant migration to the matrix during processing in the melt state. The increases in the modulus of elasticity upon organoclay (OMMT) addition were high enough to counteract the modulus decrease inherent to a 15% rubber addition. This allowed us to obtain a toughened aPA with a modulus similar to that of the unmodified aPA. The critical interparticle distance was lower in the PNs than in the corresponding blends. This decrease was attributed to the higher modulus of elasticity of the PNs matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Structure formation of polyamide 6 from the glassy state by fast scanning chip calorimetry

Fast scanning chip calorimetry has been employed to explore the kinetics of structure formation of polyamide 6 from the glassy state. First, the condition to obtain fully amorphous polyamide 6 has been evaluated. It was found that ordering processes are only permitted on cooling the relaxed melt slower than about 150Ks−1; faster cooling was connected with complete vitrification of the supercooled liquid. Cold-ordering of fully amorphous, non-aged samples on continuous heating only takes place if the heating rate is lower than 500Ks−1. Isothermal cold-ordering experiments of fully amorphous samples have been performed in a wide temperature range between 330 and 470K, in order to obtain for the first time a complete relationship between half-time of cold-ordering/crystallization and temperature. The study was completed by an initial discussion of the temperature dependence of the mechanism of nucleation and of the effect of the crystal/mesophase polymorphism on the transition kinetics.

Study on the Thermal Behaviors and the Morphology in PVP/ PA66 Blends

In this paper, PA 66 were solution blended with poly(vinyl pyrrolidone)(PVP), an amorphous polar polyamide. The thermal behaviors and morphology in the blends of polyamides (PA66)) and PVP were investigated by WAXD, DSC, FT-IR and POM methods. The equilibrium melting temperatures for PA 66 in the blends were estimated based on the linear and non-linear Hoffman-Weeks (LHW and NLHW) extrapolative methods. The interaction mode between PVP and PA66 was investigated by FT-IR spectroscopy.

Structure, thermal stability, and mechanical properties of nanocomposites based on an amorphous polyamide

AbstractPolymer nanocomposites based on an amorphous polyamide (aPA) modified with three organoclays were obtained in the melt state. The observed Tg decreases indicated that some organic modifier of the OMMT (surfactant) migrated to the matrix during mixing. The decrease in the thermal stability of the aPA in nitrogen atmosphere on organoclay addition was attributed to the instability of the organoclays. The smaller decrease in the thermal stability of the nanocomposites in air atmosphere was attributed to a barrier effect. The largest dispersion (an average of only 1.2 layers per particle) occurred using the octadecylamine‐modified organoclay (I30) that has the maximum uncovered surface; this indicates the basic importance of this parameter on exfoliation. Despite the bulky nature of the aPA that hinders the matrix/inorganic surface interactions, this dispersion level is comparable to that of semicrystalline polyamides with similar polarity. This indicates that the relation between high polarity of the matrix and high dispersion level also works in bulky aPAs, as that of this study. The significant modulus increases (56% for the nanocomposite with 5% I30) are consistent with the measured high dispersion level. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Predicting Water Sorption and Volume Swelling in Dense Polymer Systems via Computer Simulation

Atomistic model structures of amorphous polyamide 6 (PA-6) and of an adhesive system consisting of the diglycidyl ether of bisphenol A (DGEBA) as epoxy resin and isophorone diamine (IPD) as a curing agent are generated. For the adhesive, we use a new approach for the generation of the cross-linked polymer networks. It takes into account the chemical reaction kinetics of the curing reaction and, therefore, results in more realistic network structures. On the basis of the corresponding model structures, the equilibrium water content and the swelling ratio of amorphous PA-6 and of the DGEBA+IPD networks are calculated via computer simulation for different thermodynamic conditions. A hybrid method is used combining the molecular dynamics technique with an accelerated test particle insertion method. The results are in reasonable agreement with experiments and, in the case of the PA-6 system, with results obtained via other computer simulation methods.

Effect of organoclay structure and mixing protocol on the toughening of amorphous polyamide/elastomer blends

An amorphous polyamide (a-PA) was blended with an ethylene-1-octene (EOR) elastomer with organoclays present to control the elastomer particle size. Four different organoclays, M3(HT)1, M2(HT)2, M1H1(HT)2, and (HE)2M1T1 and two different mixing protocols were used to investigate the effect of the organoclay structure and mixing protocol on the morphology and properties of the resulting blends. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were used to evaluate the degree of exfoliation of the organoclays and the morphology of the elastomer particles for these blends. A detailed particle analysis was made to provide a quantitative assessment of elastomer particle size. The size and shape of the elastomer particles were dramatically affected by the amount of organoclay but the organoclay type and the mixing protocol led to slight differences. Broadly speaking, most of the MMT platelets are well exfoliated in the a-PA phase, but some locate at the interface and tend to envelop the EOR phase. The mechanical properties were not significantly affected by the organoclay type or the mixing protocol. While the organoclays reduced the EOR particles to size range where toughness might be expected, all blends proved to be brittle. A clear trade-off was observed between the Izod impact strength and tensile modulus for these blends containing organoclays.

Morphology, Phase Composition, and Molecular Mobility in Polyamide Films in Relation to Oxygen Permeability

The effect of phase composition and molecular mobility on oxygen permeability is studied for stretched films prepared from polyamide 6 (PA6) and a blend of PA6 with semiaromatic amorphous polyamide (aPA)−PA6/aPa, which is a random co-polyamide containing iso- and terephthalic chain units. The effect of stretching degree of films on crystallinity and strain-induced immobilization of the amorphous phase is studied by DSC and solid-state proton NMR transverse (T2) magnetization relaxation, respectively. Changes of these parameters upon strain are determined. Crystallinity and Tg are hardly affected by strain, as shown by DSC. Molecular mobility in the amorphous phase of stretched films is largely restricted upon increasing strain. At temperatures well above Tg, the amorphous phase consists of two fractions of nanometer thickness: one behaves like glassy polyamides, and the other one, a semirigid fraction, reveals largely hindered chain mobility. The amount of the glassy-like fraction increases proportionally to the strain. In addition, molecular mobility in the semirigid fraction decreases with increasing strain. According to high-resolution solid-state 13C NMR experiments, the composition of the semirigid fraction in PA6/aPA films is enhanced by aPA. It is shown that the immobilization of the amorphous phase has a large influence on the permeability of the films. It appears that oxygen permeability correlates well with a parameter describing strain-induced decrease in molecular mobility in the amorphous phase. This parameter is the reciprocal product of the amount of the semirigid fraction at temperatures well above Tg and molecular mobility in this fraction as determined by NMR T2 relaxation time. It is suggested that the semirigid fraction of the amorphous phase could be considered as “channels” for diffusion of oxygen molecules. Despite lower oxygen solubility in PA6 films, as shown by low-temperature proton NMR T1 relaxation data, the permeability of all PA6/aPA films under humid conditions is significantly lower than that of PA6 films. It is suggested that the lower permeability of PA6/aPA films is due to complex formation between oxygen molecules and aromatic rings of aPA, which slows down oxygen diffusion. Results of the present study are of interest for a better understanding of both permeability of polyamide films and other phenomena in polyamides that are affected by transport properties of small molecules, such as the rate of water uptake, dyeability of fibers, thermal oxidation, and blooming.

Stiffening of Polycarbonate by Addition of a Highly Dispersed and Fibrillated Amorphous Polyamide‐Based Nanocomposite

AbstractTernary systems consisting of blends of polycarbonate (PC) from bisphenol A and minority amounts of an amorphous polyamide reinforced with organically modified nanoclay (naPA), were obtained in the melt state. The nanoclay was widely exfoliated inside the dispersed naPA phase. The dispersed phase exhibited a very fine size (up to 0.36 µm), indicating compatibilization. Compatibilization was attributed to interactions between the aPA and the PC. The nanocomposite showed a lower compatibility than their corresponding blends. This lower compatibility of the nanocomposite was attributed to a hindrance of the interaction by the migrated surfactant of the organoclay. The presence of fibrillation in conjunction with a dispersed nanoclay resulted in additive enhancing effects on the modulus and yield stress. This led to modulus increases up to 46% with respect to that of the neat matrix upon the addition of 25% naPA‐10. Besides exhibiting these remarkable modulus values, these systems show an elongation at break similar to that of the neat PC matrix.magnified image

Laboratory evaluation of the resistance of plastics to the subterranean termite Coptotermes formosanus (Blattodea: Rhinotermitidae)

Since preliminary studies demonstrated unsuitability of the existing Japanese standardized methods for evaluating the termite-resistance of plastics, a new laboratory method was tested for its applicability. Assembled units, each consisting of a plastic material and a wood attachment surrounding a plastic sample, were placed around a laboratory nest of Coptotermes formosanus for 6 weeks at 28 ± 2 °C and over 80% relative humidity, and the termite attack was assessed visually. Amorphous polyamide performed best, and low-density polyethylene did worst. This new laboratory method succeeded in demonstrating termite damage to materials that are susceptible under actual service conditions, although it is not applicable to evaluating insecticide-incorporated plastics. A modified JWPA Standard No. 17 test method was employed to determine the minimum number of termites required to attack high-density polyethylene film so that it was possible to standardize the method to compare termite-resistance of non-woody materials with or without chemical treatment. It was concluded that 300 workers of C. formosanus in 12.6 cm 2 of foraging area, which was equivalent to the termite density (pressure) of 24 workers cm −2 foraging area, were required for termites to attack from a straight scratched surface.

Morphology and Mechanical Properties of Rubber Toughened Amorphous Polyamide/MMT Nanocomposites

The effects of addition of an organoclay on the morphology and the mechanical properties of blends of an amorphous polyamide (a-PA) and an elastomer (with and without grafted maleic anhydride) prepared via melt processing are reported. Transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS) were employed to obtain a detailed quantitative analyses of the morphology of the elastomer particles for these nanocomposites containing 80 wt % a-PA and 20 wt % elastomer. Stress−strain diagrams and impact strength were measured as a function of organoclay content for blends containing maleated and unmaleated elastomer. It is clear that the addition of organoclay to blends can be an effective way for reducing elastomer particle size and enhancing stiffness when the elastomer is not maleated; however, for this system, toughness is not improved in spite of these morphological changes. Blends based on the maleated elastomer give a more beneficial balance of toughness versus stiffness.

Indigo Dyeing of Polyamide Using Enzymes for Dye Reduction

Classical processes of indigo dyeing use sodium dithionite as reducing agent, causing enormous environmental problems. In this paper, a new process of indigo reduction using NADHdependent reductases from Bacillus subtilis in the presence of redox mediators is presented. The efficiency of mediated enzymatic indigo reduction on the dyeing of decitex polyamides 6 and 6,6 was studied at 60 °C, pH 7 and 11, and different indigo concentrations. The color values and color fastness properties (to wash, light and perspiration) were evaluated and compared to chemically indigo-dyed polyamides. The results indicated that the dyeing properties were pH, time and polyamide type dependent, resulting in the greater color depth of morphologically more amorphous polyamide 6,6 dyed at pH 11 for 90 minutes. Both the alkaline and acid perspiration fastness properties of the dyeings were very good, whereas the dyeings displayed poorer fastness of 3—4 to light and wash. Successful reuse of the enzyme was confirmed.

Toughening and brittle‐tough transition in blends of an amorphous polyamide with a modified styrene/ethylene‐butylene/styrene triblock copolymer

AbstractAmorphous polyamide (aPA)/maleated styrene/ethylene‐butylene/styrene triblock copolymer (mSEBS) blends with a mSEBS content up to 25% were obtained in the melt state with the aim of toughening the notch sensitive pseudoductile matrix, and of studying the parameters that influence the morphology that leads to the brittle/tough transition. The increase in the Tg of the rubbery phase, which depended on the maleinized copolymer content, indicated the presence of reacted copolymers. These copolymers should decrease the interfacial tension, thus allowing the presence of a fine dispersed particle size. The impressive (27‐fold) toughness increase observed, which is among the largest observed in toughened blends, took place at 15% mSEBS content. The critical interparticle distance (τc) of the blends was smaller than that of polyamide 6 (PA6)/mSEBS blends tested at the same conditions. Having ruled out the possible influence of other parameters, the lower τc of the aPA/mSEBS blends of this study is attributed to their higher interfacial adhesion that was inferred by the calculation of the solubility parameters and by the measured interfacial toughness. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Estudo da mobilidade molecular das blendas aPA/SAN/MMA-MA usando relaxação dielétrica

Blendas de poliamida amorfa (aPA) com copolímero de estireno-acrilonitrila (SAN) utilizando uma série de copolímeros de metil metacrilato-anidrido maleico (MMA-MA) como agente compatibilizante foram preparadas. Estes copolímeros acrílicos são miscíveis com a fase SAN, e o anidrido maleico (MA) é capaz de reagir com os grupos terminais da poliamida, levando a formação de um copolímero na interfase da blenda durante o processamento. Este estudo foca o efeito da massa molar e a concentração de anidrido maleico do compatibilizante nas propriedades de relaxação dielétrica. Os resultados mostram que tanto a concentração de anidrido maleico e a massa molar do compatibilizante influenciam a mobilidade molecular. Blendas com compatibilizantes com 5 e 10% de anidrido maleico apresentaram menor energia de ativação devido à alta mobilidade da fase SAN.

Melting behavior of a poly(ether‐block‐amide) copolymer melt‐crystallized under quiescent, isothermal conditions

AbstractSegmented poly(ether‐block‐amide) copolymers are typically known as polyamide‐based thermoplastic elastomers consisting of hard, crystallizable polyamide block and flexible, amorphous polyether block. The melting characteristics of a poly(ether‐block‐amide) copolymer melt‐crystallized under various quiescent, isothermal conditions were calorimetrically investigated using differential scanning calorimetry (DSC). For such crystallized copolymer samples, their crystalline structures under ambient condition and the structural evolutions upon heating from ambient to complete melting were characterized using ambient and variable‐temperature wide‐angle X‐ray diffractometry (WAXD), respectively. It was observed that dependent of specific crystallization conditions, the copolymer samples exhibited one, two, or three melting endotherms. The ambient WAXD results indicated that all melt‐crystallized copolymer samples only exhibited γ‐form crystals associated with the hexagonal habits of the polyamide homopolymer, whereas variable‐temperature WAXD data suggested that upon heating from ambient, a melt‐crystallized copolymer might exhibit so‐called Brill transition before complete melting. Based on various DSC and variable‐temperature WAXD experimental results obtained in this study, the applicability of different melting mechanisms that might be responsible for multiple melting characteristics of various crystallized PEBA copolymer samples were discussed. It was postulated that the low (T m1) endotherm was primarily because of the disruption of less thermally stable, short‐range ordered structure of amorphous polyamide segments of the copolymer, which was only formed after the completion of primary crystallization via so‐called annealing effects. The intermediate (Tm2) and high (Tm3) endotherms were attributed to the melting of primary crystals within polyamide crystalline microdomains of the copolymer. The appearance of these two melting endotherms might be somehow complicated by thermally induced Brill transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2035–2046, 2008

Effect of organoclay structure on morphology and properties of nanocomposites based on an amorphous polyamide

An amorphous polyamide (a-PA) and three organoclays, M3(HT)1, M2(HT)2 and (HE)2M1T1, were melt processed to explore the effect of the organoclay structure on the extent of exfoliation and properties of these nanocomposites. Wide angle X-ray scattering, transmission electron microscopy, and stress–strain behavior were used to determine the degree of exfoliation of the nanocomposites. For quantitative assessment of the structure of the nanocomposites, a detailed particle analysis was made to provide various averages of the clay dimensions and aspect ratio. The results evaluated from different methods were generally consistent with each other. Nanocomposites based on the organoclays with one alkyl tail and hydroxyl ethyl groups gave well-exfoliated structures and high matrix reinforcement while nanocomposites from two-tailed organoclay contain a considerable concentration of intercalated stacks. Nanocomposites from the organoclays with one alkyl tail showed slightly better exfoliation and matrix reinforcement than those from the organoclays with hydroxyl ethyl groups. The organoclay structure trends for a-PA are analogous to what has been observed for nylon 6; this suggests that a-PA, like nylon 6, has good affinity for the pristine silicate surface of the clay leading to better exfoliation and enhanced mechanical properties with one-tailed organoclay than multiple-tailed organoclay. Furthermore, heat distortion temperatures were predicted from the dynamic mechanical properties of nanocomposites.

The Influence of the compatibilizer Characteristics on the interfacial characteristics and phase morphology of aPA/SAN blends

The main objective of this work is study the influence of the methyl mathacrylate maleic anhydride copolymer (MMA-MA) compatibilizer properties such as molecular weight and maleic anhydride content in the characteristics of amorphous polyamide and styrene acrylonitrile copolymer (aPA/SAN) blends, correlating their interfacial characteristics and phase morphology. The blends aPA/SAN, with and without the compatibilizer, prepared were characterized by transmission electron microscopy (TEM) and small angle X-rays scattering (SAXS). The results show that the maleic anhydride concentration has a more significant effect on the blend properties than the molecular weight of the MMA-MA copolymer. Even though the system aPA/SAN is thermodynamically immiscible, it shows morphology of phases with small particles of SAN. The addition of MMA-MA copolymer with high degrees of MA led to an increase of the SAN phase particle size. With SAXS technique, it was possible to determine the interface thickness and the results shows that the characteristics of the interface do not change with the variation of the compatibilizer characteristics. The results observed in this work indicate that the viscosity ratio is very important factor on the formation of the phase morphology.

Improving the resistance to humid heat sterilization of EVOH copolymers through blending

AbstractThe effect of retorting, i.e., combined temperature and high relative humidity conditions, on the morphology, structure, and thermal characteristics of a number of extruded films containing binary and ternary blends of a 32 mol % ethylene‐vinyl alcohol copolymer (EVOH) with amorphous polyamide (aPA) and nylon‐containing ionomer as blending additives was carried out. Each film was investigated by differential scanning calorimetry, attenuated total reflectance Fourier transformed infrared spectroscopy (ATR‐FTIR), scanning electron microscopy (SEM), and synchrotron X‐ray scattering. The oxygen transmission rate of multilayer structures having as barrier element the cited blends was also measured and the results were interpreted in terms of the blends' particular structural and morphological features. From the results it was found that the thermal properties, the crystalline structure, and the water resistance of the blends were improved upon retorting compared with neat EVOH. However, only the binary blend with aPA showed a real enhancement in the oxygen barrier properties immediately after retorting compared with neat EVOH. This unprecedented and surprising effect was additionally ascribed to the retorting‐induced compatibilization between EVOH and aPA components of the blend as determined by SEM. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008